MyAccess Sign In

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

PATHOGENESIS AND EPIDEMIOLOGY

Humans are the only known reservoir of D. medinensis. They become infected by drinking unfiltered water containing copepods (plankton) that are infected with larva of D medinensis. Once ingested, the copepods die, and the infected larva are set free, penetrating the host’s stomach and intestinal wall and entering the abdominal cavity and retroperitoneal space. Maturation into adults takes 60 to 90 days, when copulation occurs, after which male worms die. It takes 8 to 12 months for the female worms to mature and migrate from the deep connective tissue to the subcutaneous tissue and then to the skin surface. The average size of the female worm is 1 m in length by 1 to 2 mm in diameter. More than 90% of the worms emerge from the lower extremities, usually below the knees. There, the female worm induces a painful blister on the skin, generally on the distal lower extremity, which ruptures and ulcerates. When this lesion comes into contact with water, which occurs frequently because infected patients immerse the limb seeking to relieve the local discomfort, the female worm emerges and releases motile larvae into the water. The larvae then might be ingested by a copepod, and if the stagnant water is used for drinking, the cycle begins again (Fig. 321–1).

Approximately 1 year after a person acquires infection from drinking contaminated water, the worm emerges through the skin, usually on the lower extremities. The worldwide campaign to eradicate dracunculiasis began in 1980 at the Centers for Disease Control and Prevention (CDC). In 1986, the World Health Assembly called for dracunculiasis elimination, and the global Guinea Worm Eradication Program (GWEP)—led by the Carter Center and supported by the World Health Organization, United Nations Children’s Fund (UNICEF), CDC, and other international organizations—began assisting the ministries of health in countries where dracunculiasis was endemic. In 1986, an estimated 3.5 million cases occurred mostly in African and Asia. Although the disease has not been completely eradicated, considerable progress has been made, and the annual numbers of reported cases in 2015 had decreased by 99%. Also in 2015, only 22 cases were reported worldwide—an 83% reduction in cases from the previous year. The disease is now limited to 4 African countries (South Sudan, Mali, Chad, and Ethiopia).